The present invention refers to a coffee machine comprising a boiler for heating the brewing water, an essentially hollow brewing cylinder having a central longitudinal axis and an open end, and a driving unit for moving the brewing cylinder along said central longitudinal axis.
A closure piston is adapted to close the open end of the brewing cylinder to thereby form a brewing chamber, and a brewing piston is located in the interior of the brewing cylinder that is movable along said central longitudinal axis to compress coffee powder received in said brewing cylinder means as well as for removing the used coffee powder cake.
In a coffee machine of this kind, principally, a coffee beverage is prepared as follows: A brewing chamber is filled with a predetermined amount of coffee powder. This coffee powder is compressed by a movable piston and, thereafter, hot water is pressed through the compressed coffee powder under high pressure. In order to close the open side of the brewing chamber, there is provided a usually stationary closure piston, whereby the brewing cylinder usually is movable with regard to the closure piston. The brewing piston adapted to compress the coffee powder is received in the interior of the brewing cylinder and is also used, besides its task to compress the coffee powder, to remove the used coffee powder cake from the brewing cylinder. For heating the brewing water, a boiler is used, from which the hot brewing water flows through a pipe to one of the two afore mentioned pistons. The relevant piston is provided with a sieve plate member. The hot brewing water is fed to that sieve plate member, thereby evenly distributed, enters the brewing chamber and evenly flows through the compressed coffee powder.